The third generation partnership project (3GPP) defines the concept of bearers. A bearer uniquely identifies traffic flows that receive a common quality of service (QoS) between a user equipment (UE) and a packet data network (PDN) gateway (PGW).
The currently standardized bearer mechanism is using bearers in the General Packet Radio Service (GPRS) tunnelling protocol (GTP) interface between the Trusted WLAN Access Network (TWAN) gateway (TWAG) and PGW but between UE and the TWAN there is only one pipe. This results in that for uplink (UL) traffic the TWAN has to classify the uplink traffic and send it on the correct bearer.
FIG. 1 is a schematic block diagram illustrating evolved packet core (EPC and evolved packet system (EPS) concepts, which are also defined in the 3GPP technical specifications (TS) 23.401 and 23.402. The figure explains the bearer concept over a 3GPP radio interface. It is noted that each PDN connection contains at least one bearer. That bearer is called default bearer. Additional bearers within that same PDN connection are called dedicated bearers. The PDN is an IP network such as the Internet or an intranet e.g. a service network. The PGW is a functional node providing access for one or more UE to one or more PDNs. The PDN connection provides a UE with an access channel to a PDN. It is a logical tunnel between UE and PGW. Each PDN connection has a single IP address or prefix. A UE can set up multiple PDN connections, possibly to the same Access Point Name (APN), a string containing the name of the PDN. The PDN connection between the PGW and the UE is further illustrated as containing a plurality of EPS bearers (three in FIG. 1). Each EPS bearer is defined by a set of IP flows with the same QoS profile. Each EPS bearer runs end-to-end (e2e) between the UE and the PGW but is a concatenation of an S5 GTP tunnel between the PGW and a serving gateway (SGW), an S1 GTP tunnel between the SGW and an evolved Node B (eNB), and a radio bearer between the eNB and the UE.
In 3GPP release 11 (Rel-11), the bearer concept is only partially implemented over Wi-Fi, since the EPS bearer concept does not exist over WLAN. FIG. 2 illustrates this. The PGW communicates via the S2a interface between the PGW and a TWAG, comprising or being associated with an access controller (AC). A PDN connection contains one or more S2a bearers (three in FIG. 2, between the PGW and the TWAG). S2a supports the bearer concept in that each bearer is a GTP tunnel. Also here there is a PDN connection between the UE and the PGW. However, WLAN does not support the bearer concept. Thus, the S2a bearer is not e2e between the UE and PGW as in access via a cellular 3GPP standard (illustrated in figure i). Instead, each PDN connection is a logical concatenation of one or more 52a tunnels between the PGW and the TWAG and a single L2 point-to-point link between the TWAG and the UE.
Different virtual media access control (MAC) addresses may be used for identifying different PDN connections over WLAN. The functional architecture is shown in FIGS. 3 and 4, where FIG. 3 illustrates the functional S2a based architecture in a non-roaming scenario and FIG. 4 illustrates the functional split of the TWAN, and where FIG. 4 zooms in what is denoted as the Trusted WLAN Access Network (TWAN) in FIG. 3. See TS 23.402 for a further clarification of this architecture. 3GPP Rel-12 allows a UE to setup multiple PDN connections over WLAN. Each PDN connection is identified by a (virtual) MAC address of the TWAG. A change request (CR) 1188 to TS 23.402, incorporated in version 12.3.0 of TS 23.402, describes how (real or virtual) MAC addresses are used to differentiate PDN connections from each other. Still, the bearer concept is not introduced over WLAN, therefore it is not possible to establish multiple bearers within the WLAN segment of the PDN connection. As a consequence, each PDN connection has a single pipe over the WLAN.